\section{Introduction}
\begin{comment}
Recently, many emerging memory technologies, such as FBDRAM, MRAM, and PRAM, are
extensively researched as the potential candidates in future memory
systems. Compared to traditional SRAM technologies, these emerging memory
technologies have the advantages of higher density, low standby power, better
scalability, etc.

Among these different technologies, the FBDRAM has attracted more and more
attention because it is totally compatible with CMOS technology and has much
higher cell density. Since the number of processing cores integrated in a single
chip keeps increasing, more on-chip memory is expected in the future memory
system. The two advantages make FBDRAM very competitive to replace SRAM as the
on-chip memory technology.
\end{comment}
The increasing number of cores integrated on a chip and the growing bandwidth
gap between on-chip memory and off-chip I/O argue for more and more on-chip
memory in future memory systems. Recently, many emerging memory technologies,
such as FBDRAM, MRAM, and PRAM, are extensively researched to attack the so
called {\em memory wall}. Compared to traditional SRAM techology, these emerging
memories have the common advantages of higher density, low standby power, better
scalability. How to use these memory candidates, however, are decided by the
process technology, performance, reliability, etc

Among these memory technologies, the FBDRAM is more competitve than others to be
used as on-chip memory because of two reasons. First, the FBDRAM has much higher
cell density than the other memory technologies. As shown in
Table~\ref{tab:size}, the cell sizes of different memory technologies are
compared. We can find that the FBDRAM has the smallest cell size. Note that
$4F^2$ is the theoritical lower bound of the one transistor~(1T) cell size ,
which is only $1/20$ of a SRAM cell size. Thus, with the same area, much more
memory can be integrated


has attracted more and more
attention because
